<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<input type="text" id="i1">
<input type="text" id="i2">
<input type="button" value="加" onclick="f(1)">
<input type="button" value="减" onclick="f(2)">
<input type="button" value="乘" onclick="f(3)">
<input type="button" value="除" onclick="f(4)">
<div>
  结果:<span></span>
</div>
<script>
    /*function f1(){
      let i1 = document.querySelector("#i1");
      let i2 = document.querySelector("#i2");
      let s = document.querySelector("span");
      s.innerText=i1.value*1+i2.value*1;
    }
    function f2(){
      let i1 = document.querySelector("#i1");
      let i2 = document.querySelector("#i2");
      let s = document.querySelector("span");
      s.innerText=i1.value-i2.value;
    }
    function f3(){
      let i1 = document.querySelector("#i1");
      let i2 = document.querySelector("#i2");
      let s = document.querySelector("span");
      s.innerText=i1.value*i2.value;
    }
    function f4(){
      let i1 = document.querySelector("#i1");
      let i2 = document.querySelector("#i2");
      let s = document.querySelector("span");
      s.innerText=i1.value/i2.value;
    }*/
    function f(x){
      // let i1 = document.querySelector("#i1");
      // let i2 = document.querySelector("#i2");
      let s = document.querySelector("span");
      switch (x){
        case 1:
          s.innerText = i1.value*1 + i2.value*1;
          break;
        case 2:
          s.innerText = i1.value - i2.value;
          break;
        case 3:
          s.innerText = i1.value * i2.value;
          break;
        case 4:
          s.innerText = i1.value / i2.value;
          break;
      }
    }
</script>
</body>
</html>